Alpha-linolenic acid and its conversion to longer chain n-3 fatty acids: benefits for human health and a role in maintaining tissue n-3 fatty acid levels

Prolonged QT interval and lipid alterations beyond β-oxidation in very long-chain acyl-CoA dehydrogenase null mouse hearts

Patients with very long-chain acyl-CoA dehydrogenase (VLCAD) deficiency frequently present cardiomyopathy and heartbeat disorders. However, the underlying factors, which may be of cardiac or extra cardiac origins, remain to be elucidated. In this study, we tested for metabolic and functional alterations in the heart from 3- and 7-mo-old VLCAD null mice and their littermate counterparts, using validated experimental paradigms, namely, 1) ex vivo perfusion in working mode, with concomitant evaluation of myocardial contractility and metabolic fluxes using (13)C-labeled substrates under various conditions; as well as 2) in vivo targeted lipidomics, gene expression analysis as well as electrocardiogram monitoring by telemetry in mice fed various diets. Unexpectedly, when perfused ex vivo, working VLCAD null mouse hearts maintained values similar to those of the controls for functional parameters and for the contribution of exogenous palmitate to β-oxidation (energy production), even at high palmitate concentration (1 mM) and increased energy demand (with 1 μM epinephrine) or after fasting. However, in vivo, these hearts displayed a prolonged rate-corrected QT (QTc) interval under all conditions examined, as well as the following lipid alterations: 1) age- and condition-dependent accumulation of triglycerides, and 2) 20% lower docosahexaenoic acid (an omega-3 polyunsaturated fatty acid) in membrane phospholipids. The latter was independent of liver but affected by feeding a diet enriched in saturated fat (exacerbated) or fish oil (attenuated). Our finding of a longer QTc interval in VLCAD null mice appears to be most relevant given that such condition increases the risk of sudden cardiac death.

Health benefits of marine foods and ingredients

The health benefits of seafood consumption have primarily been associated with protective effects against cardiovascular diseases (CVD). However, intake of seafood has also been associated with improved foetal and infant development, as well as several other diseases and medical conditions. The health promoting effects have chiefly been attributed to the long-chain n-3 polyunsaturated fatty acids (n-3 PUFA), eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA). In addition, the general fatty acid profile is considered favourable. On the other hand, recent and emerging research on seafood proteins and other seafood derived components suggest that these nutritional components contribute to the health effects. In this paper we review the nutritional characteristics and health benefits of marine foods and ingredients, and discuss some current and future trends in marine food production.

Significance of phenolic compounds in tropical forages for the ruminal bypass of polyunsaturated fatty acids and the appearance of biohydrogenation intermediates as examined in vitro

The purpose of the present study was to assess the influence of phenol-rich tropical ruminant feeds on the extent of ruminal biohydrogenation (BH) of polyunsaturated fatty acids (PUFA). Samples of 27 tropical forages (mainly tree and shrub leaves), characterised by different phenolic profiles, were incubated in vitro (n = 4 replicates) with buffered rumen fluid for 24 h using the Hohenheim gas test method. Linseed oil was added as a rich source of PUFA. In the plants, total extractable phenols (TEP), non-tannin phenols, condensed tannins, and fatty acids were determined. After terminating incubation, the fatty acid profile present in fermentation fluid (total syringe content) was analysed by gas chromatography. The relationship between TEP and the disappearance of α-linolenic acid from the incubation fluid was negative (R2 = 0.48, P < 0.001), indicating that TEP reduced the ruminal BH of this PUFA. Similarly, TEP were negatively related with the disappearances of linoleic acid (R2 = 0.52, P < 0.001) and oleic acid (R2 = 0.58, P < 0.001). The appearance of rumenic acid, an important conjugated linoleic acid isomer, was positively correlated with TEP (R2 = 0.30, P < 0.01), while the opposite result was seen with stearic acid (R2 = 0.22, P < 0.05). Leaves of avocado (Persea americana) were particularly interesting, because they changed the BH pattern at a moderate TEP content of 73 g/kg DM. It is concluded that, in the tropical feedstuffs investigated, TEP have an impact on ruminal fatty acid BH and are associated with an increased bypass of PUFA and the generation of conjugated linoleic acid.

Dietary intake and status of n-3 polyunsaturated fatty acids in a population of fish-eating and non-fish-eating meat-eaters, vegetarians, and vegans and the product-precursor ratio [corrected] of α-linolenic acid to long-chain n-3 polyunsaturated fatty acids: results from the EPIC-Norfolk cohort

BACKGROUND

Intakes of n-3 (omega-3) polyunsaturated fatty acids (PUFAs) are important for health. Because fish is the major source of eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA), non-fish-eaters may have suboptimal n-3 PUFA status, although the importance of the conversion of plant-derived α-linolenic acid (ALA) to EPA and DHA is debated.

OBJECTIVE

The objective was to determine intakes, food sources, and status of n-3 PUFAs according to dietary habit (fish-eaters and non-fish-eating meat-eaters, vegetarians, or vegans) and estimated conversion between dietary ALA and circulating long-chain n-3 PUFAs.

DESIGN

This study included 14,422 men and women aged 39-78 y from the EPIC (European Prospective Investigation into Cancer and Nutrition)-Norfolk cohort with 7-d diary data and a substudy in 4902 individuals with plasma phospholipid fatty acid measures. Intakes and status of n-3 PUFAs were measured, and the product-precursor ratio [corrected] of ALA to circulating n-3 PUFAs was calculated.

RESULTS

Most of the dietary intake of EPA and DHA was supplied by fish; however, meat was the major source in meat-eaters, and spreading fats, soups, and sauces were the major sources in vegetarians. Total n-3 PUFA intakes in non-fish-eaters were 57-80% of those in fish-eaters, but status differences were considerably smaller [corrected]. The estimated product-precursor ratio [corrected] was greater in women than in men and greater in non-fish-eaters than in fish-eaters.

CONCLUSIONS

Substantial differences in intakes and in sources of n-3 PUFAs existed between the dietary-habit groups, but the differences in status were smaller than expected, possibly because the product-precursor ratio [corrected] was greater in non-fish-eaters than in fish-eaters, potentially indicating increased estimated conversion of ALA. If intervention studies were to confirm these findings, it could have implications for fish requirements.

Lipid classes and fatty acid patterns are altered in the brain of γ-synuclein null mutant mice

The well-documented link between α-synuclein and the pathology of common human neurodegenerative diseases has increased attention to the synuclein protein family. The involvement of α-synuclein in lipid metabolism in both normal and diseased nervous system has been shown by many research groups. However, the possible involvement of γ-synuclein, a closely-related member of the synuclein family, in these processes has hardly been addressed. In this study, the effect of γ-synuclein deficiency on the lipid composition and fatty acid patterns of individual lipids from two brain regions has been studied using a mouse model. The level of phosphatidylserine (PtdSer) was increased in the midbrain whereas no changes in the relative proportions of membrane polar lipids were observed in the cortex of γ-synuclein-deficient compared to wild-type (WT) mice. In addition, higher levels of docosahexaenoic acid were found in PtdSer and phosphatidylethanolamine (PtdEtn) from the cerebral cortex of γ-synuclein null mutant mice. These findings show that γ-synuclein deficiency leads to alterations in the lipid profile in brain tissues and suggest that this protein, like α-synuclein, might affect neuronal function via modulation of lipid metabolism.

Bovine adipose triglyceride lipase is not altered and adipocyte fatty acid-binding protein is increased by dietary flaxseed

In this paper, we report the full-length coding sequence of bovine ATGL cDNA and analyze its expression in bovine tissues. Similar to human, mouse, and pig ATGL sequences, bovine ATGL has a highly conserved patatin domain that is necessary for lipolytic function in mice and humans. This suggests that ATGL is functionally intact as a triglyceride lipase in cattle. Tissue distribution of ATGL gene expression was highest in fat and muscle (skeletal and cardiac) tissue, while protein expression was solely detectible in the adipose tissue. The effect of 109 days of flaxseed supplementation on ATGL and adipocyte fatty acid-binding protein (FABP4 or A-FABP, E-FABP or FABP5) expression was examined in Angus steers. Supplemented steers had greater triacylglycerol (TAG) content in the muscle compared with unsupplemented ones. Additionally, supplementation increased A-FABP expression and decreased stearoyl-CoA desaturase 1 (SCD-1) expression in muscle, while total ATGL expression was unaffected. In summary, supplementation of cattle rations with flaxseed increased muscle TAG concentrations attributed in part to increased expression of key enzymes involved in lipid trafficking (A-FABP) and metabolism (SCD-1).

Characterization of rapeseed (Brassica napus) oils by bulk C, O, H, and fatty acid C stable isotope analyses

Rapeseed ( Brassica napus ) oils differing in cultivar, sites of growth, and harvest year were characterized by fatty acid concentrations and carbon, hydrogen, and oxygen stable isotope analyses of bulk oils (delta(13)C(bulk), delta(2)H(bulk), delta(18)O(bulk) values) and individual fatty acids (delta(13)C(FA)). The delta(13)C(bulk), delta(2)H(bulk), and delta(18)O(bulk) values were determined by continuous flow combustion and high-temperature conversion elemental analyzer-isotope ratio mass spectrometry (EA/IRMS, TC-EA/IRMS). The delta(13)C(FA) values were determined using gas chromatography--combustion-isotope ratio mass spectrometry (GC/C/IRMS). For comparison, other C(3) vegetable oils rich in linolenic acid (flax and false flax oils) and rich in linoleic acid (poppy, sunflower, and safflower oils) were submitted to the same chemical and isotopic analyses. The bulk and molecular delta(13)C values were typical for C(3) plants. The delta(13)C value of palmitic acid (delta(13)C(16:0)) and n-3 alpha-linolenic acid (delta(13)C(18:3n-3)) differed (p < 0.001) between rape, flax, and poppy oils. Also within species, significant differences of delta(13)C(FA) were observed (p < 0.01). The hydrogen and oxygen isotope compositions of rape oil differed between cultivars (p < 0.05). Major differences in the individual delta(13)C(FA) values were found. A plant-specific carbon isotope fractionation occurs during the biosynthesis of the fatty acids and particularly during desaturation of C(18) acids in rape and flax. Bulk oil and specific fatty acid stable isotope analysis might be useful in tracing dietary lipids differing in their origin.

Transfer of linoleic and linolenic acid from feed to milk in cows fed isoenergetic diets differing in proportion and origin of concentrates and roughages

The transfer of ingested alpha-linolenic acid (ALA) and linoleic acid (LA) determines the nutritional quality of milk, but the factors determining this transfer are unclear. The present experiment investigated the influence of roughage to concentrate proportions and the effect of concentrate types on milk fat composition. Respectively, six lactating dairy cows were fed one of three isoenergetic (5.4+/-0.05 MJ net energy for lactation/kg dry matter; DM) and isonitrogenous (215+/-3.5 g crude protein/kg DM) diets, consisting of ryegrass hay only (33 g fatty acids/kg DM; ALA-rich, no concentrate), maize (straw, whole maize pellets and gluten; 36 g fatty acids/kg DM; LA-rich; 560 g concentrate/kg DM), or barley (straw and grain plus soybean meal; 19 g fatty acids/kg DM; LA-rich; 540 g concentrate/kg DM). The fatty acid composition of feeds and resulting milk fat were determined by gas chromatography. The ALA concentration in milk fat was highest (P<0.001) with the hay-diet, but the proportionate transfer of ALA from diet to milk was lower (P<0.001) than with the maize- or barley-diets. The LA concentration in milk fat was highest with the maize-diet (P<0.05, compared with hay) but relative transfer rate was lower (P=0.01). The transfer rates of ALA and LA were reciprocal to the intake of individual fatty acids which thus contributed more to milk fat composition than did roughage to concentrate proportions. The amount of trans-11 18:1 in milk fat was lowest with the barley-diet (P<0.001) and depended on the sum of ALA and LA consumed. The milk fat concentration of cis-9, trans-11 18:2 (rumenic acid) was more effectively promoted by increasing dietary LA (maize) than ALA (hay). Amounts of 18:0 secreted in milk were four (maize) to seven (hay) times higher than the amounts ingested. This was suggestive of a partial inhibition of biohydrogenation in the maize-diet, possibly caused by the high dietary LA level.

Elevated production of docosahexaenoic acid in females: potential molecular mechanisms

Observational evidence suggests that in populations consuming low levels of n-3 highly unsaturated fatty acids, women have higher blood levels of docosahexaenoic acid (DHA; 22:3n-6) as compared with men. Increased conversion of alpha-linolenic acid (ALA; 18:3n-3) to DHA by females has been confirmed in fatty acid stable isotope studies. This difference in conversion appears to be associated with estrogen and some evidence indicates that the expression of enzymes involved in synthesis of DHA from ALA, including desaturases and elongases, is elevated in females. An estrogen-associated effect may be mediated by peroxisome proliferator activated receptor-alpha (PPARalpha), as activation of this nuclear receptor increases the expression of these enzymes. However, because estrogens are weak ligands for PPARalpha, estrogen-mediated increases in PPARalpha activity likely occur through an indirect mechanism involving membrane-bound estrogen receptors and estrogen-sensitive G-proteins. The protein kinases activated by these receptors phosphorylate and increase the activity of PPARalpha, as well as phospholipase A(2) and cyclooxygenase 2 that increase the intracellular concentration of PPARalpha ligands. This review will outline current knowledge regarding elevated DHA production in females, as well as highlight interactions between estrogen signaling and PPARalpha activity that may mediate this effect.